This invention relates to an angle detector device for detecting the angular position or orientation of a semiconductor wafer, and especially to an angle detector device for a precise determination of the angular position of a silicon wafer with respect to the crystal axes thereof in a photolithography step in the LSI production process.
In the production of LSI's, etc., fine patterns are formed on silicon wafers by means of photolithography. Before the photoresist on the wafer is exposed in the photolithography process, the angular position of the wafer must be determined and adjusted so that the photolithography exposure pattern is aligned with the crystal axes of the wafer.
Referring first to FIG. 1, let us describe a conventional method for determining the angular position of a silicon wafer 30 around its central axis. A disk-shaped silicon wafer 30 is supported on a holder (not shown) rotatable in the direction 31. The determination of the angular position of the wafer 30 is effected by means of a flat surface 32 (referred to hereinafter as orientational flat) formed on the edge of the wafer. A laser oscillator 33 generates a laser beam 34 directed toward a peripheral portion of wafer 30. The wafer 30 is rotated while the laser beam 34 irradiates on the edge of the wafer 33. The laser beam 34 is transmitted through the edge of the wafer 30 and hence is received by a photosensor 35 opposing the laser oscillator 33 only when the wafer 30 is at such a rotational position that the laser beam 34 falls on the orientational flat 32. Thus, the angular position of the wafer 30 can be determined and adjusted on the basis of the profile of the output signal of the photosensor 35.
The above method of detecting the angular position of silicon wafers, however, has the following disadvantage. Namely, according to the above conventional method, the determination of the directions of the crystal axes of the wafer is effected only indirectly by means of the orientational flat 32. Thus precise alignment of the crystal axes of the wafer to the photolithography pattern is hard to effect. In addition, the precision of the angular position of the wafer in the photolithography step is further reduced due to the fact that the wafer may be moved a number of times after the angle thereof is set.